There was laughter from friends of Oscar Pistorius when Hilton Botha claimed the runner would risk fleeing South Africa, despite his celebrity.
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Nearly 1,000 properties have been left without power, and road users have been warned of potentially hazardous conditions.
It follows a surprise summit between South Korea's Moon Jae-in and the North's Kim Jong-un.
Organisers issued a warning about a “dangerous high strength or bad batch substance on site”.